1. Field of the Invention
The present invention relates to an apparatus for automatically adjusting a light axis or a lighting area of a light beam emitted from a vehicle headlight on the basis of a steering angle of a steering wheel.
2. Description of Related Art
An apparatus for automatically adjusting directions of light axes of vehicle headlights is constituted by actuators for swiveling horizontally or vertically the vehicle headlights, an ECU (Electronic Control Unit) calculating swiveling or leveling angles of the vehicle headlights based on the signals received from the sensors mounted on the vehicle for detecting the attitude or state of the vehicle such as a steering angle sensor, vehicle height sensors, and a vehicle speed sensor. Such an apparatus has to be provided with fail-safe protection mechanism against failure or abnormality in theses sensors or a communication network, for example, a CAN (Controller Area Network) within the vehicle in order to enable returning the light axes of the vehicle headlights to the initial direction or straight forward direction, or lighting an alarm lamp when the failure or abnormality occurs.
Japanese Utility Model Application Laid-Open No. 6-42409 discloses a technique for directing forcibly the light axes of the vehicle headlights straight forward in response to the driver's manipulation of a specific manual switch when the steering angle sensor develops trouble.
According to this technique, if the steering angle sensor develops trouble while the vehicle is turning right, for example, the light axes of the vehicle headlights are returned to the straight forward direction promptly. This fail-safe action is represented by a curved arrow AR in FIG. 7 illustrating a vehicle making a right turn.
This fail-safe action causes an abrupt shift of the lighting area of the vehicle headlights from the swivel-controlled position represented by the dotted line to the straight forward position represented by the solid line. Since the direction of this shift is opposite to the turning direction of the vehicle, the driver feels odd and the visibility in the forward direction becomes worse. In addition, if the steering angle sensor is restored, the position of the lighting area of the vehicle headlights may shift abruptly again, because the swivel control on the light axes of the vehicle headlights resumes promptly after the restoration of the steering angle sensor. The drive feels odd also then.